Leak reducing radial piston pump or motor

ABSTRACT

A radial piston pump or motor having means for reducing leakage across the pintle lands.

United States Patent Tobias 1 1 Jan. 25, 1972 [541 LEAK REDUCING RADIAL PISTON References Cited PUMP 0R MOTOR UNITED STATES PATENTS [72] Inventor: Jaromir Tobias, Box 141, Road #2, 3 279 390 10/1966 Hoflacher 91/6 5 Rhnebeck' 2572 3,173,376 3/1965 Hulman et al. ..91/488 22 Filed; Apr, 2 1970 1,987,781 1/1935 Maw ..9l/498 [21] Appl. No.: 31,680 Primary Examinerwill iam L. Freeh Related U.S Applicafion Dam Attorney-Mark T. Basseches and Paula T. Basseches [63] Continuation of Ser. N0. 795,325, Jan. 30, 1969, Pat. ABSTRACT U.S. Cl ..91/498 Int. Cl ..F04b 1/24 Field of Search ..91/491, 484, 498

A radial piston pump or motor having means for reducing leakage across the pintle lands.

2 Claims, 3 Drawing Figures PATENTEU JAN25 I972 JAROMIR TOBIAS BY M M ATTORNEY LEAK REDUCING RADIAL PISTON PUMP OR MOTOR This application is a continuation of my application Ser. No. 795,325, filed Jan. 30, 1969 entitled Low Friction Radial Piston Pump Or Motor.

BACKGROUND OF THE INVENTION This invention is in the field of radial piston pumps and motors.

Devices of this sort conventionally include a pintle shaft having opposed cutout areas defining open charge and discharge chambers. The charge and discharge chambers are separated at the periphery of the shaft by arcuate land areas. The cylinder block rotates about the shaft, the ports of the cylinder block progressively being aligned with one said chamber and, upon continued rotation, traversing a land and thereafter being communicated with the other said chamber.

It will be appreciated that pintle shafts normally include two such lands, the arcuate extent of the lands being sufficient completely to seal the ports in the cylinder block as the ports traverse the lands. Substantial leakage across the lands from the high-pressure chamber to the lowpressure chamber is encountered in all radial piston pumps or motors. The leakage occurs in the space defined between the outer surface of the arcuate lands and the inner surface of the cylinder block which rides over the lands. The amount of leakage, of course, depends upon pressure and tolerance factors but, in all instances, such leakage is significant.

SUMMARY OF THE INVENTION The invention may be summarized as directed to a leakagereducing means for use with a hydraulic pump or motor of the radial piston type.

In accordance with the invention, the arcuate land surface is provided with at least one axially extending groove on its outer surface, which groove is of substantially capillary dimensions, i.e., from about 0.002 inch to about 0.010 inch. Unexpectedly, by the provision of such groove, the leakage across the space between the outer arcuate surface of the land and the inner surface of the axial bearing in the cylinder block is considerably reduced.

Optionally, the arcuate segment may be fabricated of separate metal components and may be inserted or affixed onto portions of the pintle assembly.

Accordingly, it is an object of the invention to provide a radial piston pump or motor which exhibits improved leakage loss characteristics across the lands between the charge and the discharge areas of the pintle shaft.

It is a further object of the invention to provide an improved radial piston pump or motor device wherein the external surface of the land areas is provided with axially extending grooves of substantially capillary cross-sectional dimension for purposes of reducing leakage across the clearance area between the lands and the cylinder block.

To attain these objects and such further objects as may appear herein or be hereinafter pointed out, reference is made to the accompanying drawings, forming a part hereof, in which:

FIG. I is a vertical section through a radial piston pump or motor device, which has been illustrated diagrammatically.

FIG. 2 is a magnified sectional view of the mating area between the land of the pintle shaft and the interior internal bore of the cylinder block.

FIG. 3 is a plan view of the land area of the pintle shaft.

Reference will now be made to the drawings wherein the device includes a radial piston pump or motor including a frame 11 supporting a housing 12. The housing 12 may be shifted transversely with respect to the legs l3, 14 of the frame 11 by a threaded handle 15, it being understood that this function is normally effected by a servo-controlled or other automatic mechanism. The transverse shifting function is conventional in apparatus of this sort having variable displacement and is employed to vary the eccentricity of the reaction ring 16 with respect to the pintle shaft.

The pintle shaft 17, as is conventional, is cylindrical throughout the major portion of its length and is provided with outwardly open charge and discharge chambers 18 and [9, formed by cutting away central portions of the shaft. In the usual manner, the pintle shaft includes axially directed bores 20, 21 communicating with the chambers I8, 19, respectively, it being understood that the conduits 20, 21 extend to the exterior of the pump or motor where appropriate connections are made in accordance with the intended use of the device.

A cylinder block 22 is rotatably mounted on the pintle shaft [7 and includes an axially extending inner bore 23 which is rotatably received over the pintle shaft. The axial dimension of the block 22 at the bore 23 exceeds the axial length of the charge and discharge chambers I8, 19 so that the axial extremities of the bore defining portions of the block engage against continuous cylindrical portions of the pintle shaft, to prevent leakage axially beyond the discharge and charge areas.

The block is provided, in the usual manner, with a plurality of cylinder bores 24, within each of which is mounted a piston 25, the pistons being free to reciprocate within the bores.

The outer ends 26 of the pistons press against an annular track 27 on the inner face of the reaction ring 16. The pistons reciprocate within the cylinders in accordance with the eccentricity of the reaction ring as respects the pintle axis, in a wellknown manner.

The cylinder bores 24, at their innermost terminal ends, define ports 28 to provide communication between the cylinders and the charge and discharge areas or chambers 18 and 19, such that as the block rotates about the shaft, each port is sequentially communicated with the charge area and the discharge area.

Optionally but preferably, in accordance with my US. Pat. No. 3,345,916 ofOct. I0, 1967, the ports may be axially elongated but reduced in a transverse dimension so as to make most efficient use of the cylinder block area, as taught in the aforesaid patent.

The pintle shaft 17, in the area between the charge and discharge portions 18 and 19, is provided with arcuate land areas 29 whose outer radius of curvature matches the inner radius of curvature of the bore 23 of the block. The angular or transverse extent of the outer arcuate surface 30 of the lands 29 must exceed the arcuate dimension or angular extent of the ports so that, as each port traverses a land, it will be sealed and cannot span the land.

As heretofore described, the radial piston pump or motor is known and, thus, detailed descriptions of the various elements have been avoided.

I have discovered that the leakage across the area defined by the outer arcuate surface 30 of the lands 29 and the inner bore 23 of the block which has always been experienced in devices of this sort can be drastically reduced by forming one or more axially extending grooves 31 on the outer surface 30 of the lands 29. Unexpectedly, such groove or grooves, which are preferably of capillary cross section, reduce or inhibit, in some manner, the flow of fluid across the surface 30.

The precise mechanics of the flow reduction resulting from the use of the grooves is not known, nor have any of the theories advanced in explanation of this phenomenon been fully corroborated. The most logical explanation offered is that, in the usual rotary apparatus, leakage takes the form of a laminar flow across the land surfaces. The capillary grooves are believed in some manner to interrupt the laminar flow by creation of a turbulence and/or to exert some fonn of outward pressure against the internal bore of the cylindrical block. In any event, the capillary grooves do provide a reduction in the flow or leakage losses across the arcuate lands, resulting in an improvement in efficiency of the apparatus.

The lands may, of course, be formed integrally with the remainder of the pintle shaft or, in accordance with the illustrations, may constitute added segments of the same or of a different metallic material formed with an inwardly facing groove 32 seated on an outwardly directed rib or ridge 33 of the pintle shaft 17.

From the foregoing it will be appreciated that there is provided herein an improved radial piston pump or motor apparatus characteiizedby reduced leakage losses in the flow across the lands separating the highand low-pressure discharge areas of the pintle shaft. The improvement is the result of the provision of one or more generally axially extending grooves of capillary dimension on the outwardly facing arcuate land surfaces.

Having thus described the invention and illustrated its use, what is claimed as new and is desired to be secured by Letters Patent is:

1. lo a radial piston pump or motor apparatus of the type which comprises a pintle shaft having a fluid distribution section including opposed, outwardly open, highand low-pressure discharge and charge areas, and arcuate land portions separating said areas, and a cylinder block having an axially directed central bore rotatably mounted in registry with said distribution section, said block including cylinder bores tcrminating at inwardly opening ports at said central bore, said ports being sequentially communicated with said highand said low-pressure charge and discharge areas as said block rotates about said shaft and being sealed as said ports traverse said lands, said apparatus being characterized by said lands each including at least one generally axially directed groove on the outer face thereof, the longitudinal extent of said groove being at least substantially coextensive with the length of said lands, the cross section of said groove being of substantially capillary dimensions.

2. The device of claim 1 wherein said arcuate land portions comprise separable and replaceable elements adapted to be mounted on said pintle shaft. 

1. In a radial piston pump or motor apparatus of the type which comprises a pintle shaft having a fluid distribution section including opposed, outwardly open, high- and low-pressure discharge and charge areas, and arcuate land portions separating said areas, and a cylinder block having an axially directed central bore rotatably mounted in registry with said distribution section, said block including cylinder bores terminating at inwardly opening ports at said central bore, said ports being sequentially communicated with said high- and said low-pressure charge and discharge areas as said block rotates about said shaft and being sealed as said ports traverse said lands, said apparatus being characterized by said lands each including at least one generally axially directed groove on the outer face thereof, the longitudinal extent of said groove being at least substantially coextensive with the length of said lands, the cross section of said groove being of substantially capillary dimensions.
 2. The device of claim 1 wherein said arcuate land portions comprise separable and replaceable elements adapted to be mounted on said pintle shaft. 